Analysis of amplitude modulation atomic force microscopy in aqueous salt solutions

Highlights: • Imaging contrast during AM-AFM performed in salt solutions is numerically analyzed. • Imaging contrast is only marginally improved (∼15%) at high amplitude setpoints. • Sample indentation and maximum interaction force values remain relatively unaffected. - Abstract: We present a numerical analysis of amplitude modulation atomic force microscopy in aqueous salt solutions, by considering the interaction of the microscope tip with a model sample surface consisting of a hard substrate and soft biological material through Hertz and electrostatic double layer forces. Despite the significant improvements reported in the literature concerning contact-mode atomic force microscopy measurements of biological material due to electrostatic interactions in aqueous solutions, our results reveal that only modest gains of ∼15% in imaging contrast at high amplitude setpoints are expected under typical experimental conditions for amplitude modulation atomic force microscopy, together with relatively unaffected sample indentation and maximum tip–sample interaction values